This invention relates to the fabrication of magnetic data transducing heads, and particularly to treating the surfaces of such heads having magnetic ceramic cores.
The ongoing effort to increase data storage capacities of magnetic discs and other media is directed primarily to increasing the density at which data can be stored. Greater density leads to stricter tolerances for the fabrication of transducing heads, particularly with respect to critical dimensions such as flux gap width and throat height.
As to gap width, U.S. Pat. No. 4,279,102 (Hennenfent) discloses a method for manufacturing narrow track ferrite head cores. A grinding wheel, mounted with extreme care to virtually eliminate radial and axial run-out, is used to cut a series of slots or kerfs in a ferrite bar. The slots form narrow projections, one associated with each core. Each projection includes the flux gap and affords control over the gap width. A liquid coolant jet is provided at the point of grinding wheel cutting.
In U.S. Pat. No. 4,670,972 (Sakakima), a magnetic layer is either sputtered or evaporated onto glass or other non-magnetic substrate. A second substrate is bonded to the first, with the sputtered layer providing a magnetic gap. Magnetic material then is sputtered or evaporated onto the bonded substrates to a predetermined thickness. The magnetic layers then are lapped to expose an edge of gap filling layer between adjacent magnetic layers. Grinding, lapping and polishing, particularly with reference to present-day magnetic ceramic materials, is not discussed in any detail. Since the gap filling layer is formed by sputtering, magnetic gap length is said to be precisely determined. Further, the thickness of the magnetic layers determines the gap width.
Other techniques are known, although not specifically related to fabricating magnetic heads. For example, U.S. Pat. No. 3,485,608 (Olin) discloses a slurry for polishing silicon slices, as opposed to magnetic ceramic materials where permeability is a paramount concern. The slurry has a diamond grit, and is pH controlled in the range of from nine to twelve, so that chemical etching proceeds simultaneously with polishing.
Certain ferrite materials used in the fabrication of transducing heads, and particularly cores, are known as magnetic ceramics. Such materials, e.g. manganese zinc ferrite (MnZn) and nickel zinc ferrite (NiZn) are particularly well suited as the core material in composite heads or in the construction of monolithic heads, due to their relatively high magnetic permeability and low coercivity.
At the same time, these magnetic ceramics are subject to damage from abrading and other surface treating techniques. It has been found that MnZn and NiZn ferrites are subject to multiple crystal dislocations and plastic deformation due to diamond grit lapping processes, which reduce the permeability near the article surface and create a layer of residual compressive stresses, referred to as a deformed layer or "dead layer". A known approach to reduce the dead layer is a chemical or electro-chemical etching, for which is disclosed a tin lapping plate with concentric circular grooves, submerged in a fluid, principally water containing about five percent silicon dioxide (SiO.sub.2) particles of about seventy Angstroms in diameter.
It has been found that the deformed layer not only degrades magnetic properties, but increases surface cracking due to residual compressive stresses in the deformed layer, causing tensile stresses in regions near the deformed layer. Micro surface hardness (hardness of the surface layer) becomes non-uniform due to the creation of soft spots when the crystalline layer is deformed. The magnetic ceramic surface becomes more sensitive to heat, and oxides are formed during grinding and lapping operations which further contribute to the deformed layer.
Therefore, it is an object of the present invention to provide a process for fabricating transducing heads in a manner to substantially reduce the thickness of the deformed layer in magnetic ceramic materials.
Another object is to provide a composite head with improved magnetic permeability and signal amplitude.
Another object of the invention is to reduce crystalline dislodging at the surface of composite and/or monolithic transducing heads, to reduce the friction and resultant wear at the interface between discs and heads.
Yet another object is to increase the useful life of magnetic data reading and recording systems by fabricating a slider with more uniform micro hardness.